Disc drives are digital data storage devices which store and retrieve large amounts of user data in a fast and efficient manner. The data are magnetically recorded on the surfaces of one or more rigid data storage discs affixed to a spindle motor for rotation at a constant high speed. The discs and spindle motor are commonly referred to as a disc stack.
The disc stack is accessed by an array of aligned data transducing heads which are controllably positioned by an actuator assembly. Each head typically includes electromagnetic transducer read and write elements which are carried on an air bearing slider. The slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly each head in a closely spaced relationship to the disc surface.
A typical actuator assembly includes a central body which pivots about an actuator axis adjacent the outermost diameter of the disc stack. Rigid actuator arms project from the central body into the disc stack, and flexible suspension assemblies (flexures) project from the ends of the actuator arms to support the heads.
The flexures bias the heads toward the disc surfaces and include gimbal features that allow the heads to rotate about three axes (pitch, yaw and roll). Each set of heads, gimbals and flexures is referred to as a head gimbal assembly (HGA). The HGAs are affixed to the ends of the actuator arms using any number of suitable processes including swaging, adhesive, compression (with split actuator arms), etc.
An actuator coil of a voice coil motor (VCM) projects from the central body substantially opposite the actuator arms and is immersed in a magnetic field of the VCM. Application of current to the coil causes the actuator to pivot about the actuator axis and move the heads across the disc surfaces. A servo control circuit uses embedded servo data written to the discs to detect head position and generate the requisite coil current to adjust the positions of the heads as desired during operation.
One common prior art approach to writing servo data has involved installing the discs into a disc drive and using a servo track writer (STW) to write the servo data to the discs. Current generations of disc drives are increasingly using multiple disc writer (MDW) stations to write the servo data to the discs at a production facility prior to installation of the discs into the drives.
An MDW station operates similarly to a disc drive but makes use of several actuator assemblies and several discs to achieve increased production efficiencies. An MDW station can also write the servo data in a gaseous environment having a lower density than ambient air (such as helium) in order to achieve higher yields and/or faster throughput. A typical MDW of the current generation has a capacity on the order of around 10-15 discs. As with disc drives, MDW stations use actuator assemblies with actuator arms and HGAs to write the servo data to the discs.
Specially configured tooling is typically used to install an HGA onto an actuator arm (whether for a disc drive actuator or an MDW actuator). To support the HGA during installation, a support element (spacer key) fits against a base plate of the HGA while the HGA is being attached to the actuator arm.
A presently utilized spacer key configuration has a “compression-slit” design. For this design, the spacer key is essentially a beam with a longitudinal slit along a length of the beam, dividing the beam into an upper section and a lower section. The size of the slit in the spacer key is selected so that the upper and lower sections can be slightly deflected one toward another.
The purpose of the compression-slit design is to account for a difference in a size of a gap between two opposed actuator arms. A first gap size exists when installing a first HGA to the first actuator arm. A second gap size exists when attaching a second HGA to the opposed second actuator arm because the second gap size will differ from the first gap size by a thickness of the HGA.
Problems have arisen with the use of the spacer key of the compression-slit design. As a compromise between two gap sizes, the spacer key typically does not quite fit either gap size properly and thus fails to completely bias the HGAs flush with either actuator arm. Also, after many uses, the spacer key can lose elasticity and thus does not return to the original spacing size.
Thus, the spacer key does not provide full contact with a baseplate of the HGA, which causes the HGAs to be skewed with respect to the actuator arms. This in turn causes relatively large differences to occur in the actuator arm spacing. As a result, the HGAs are not seated flush against the actuator arms and can loosen or become detached during subsequent use.
Although spacer keys of the existing art have been found operable, there remains a continued need in the art for improved configurations that overcome these and other limitations of the existing art.